Many microsurgical procedures require precision cutting and/or removal of various body tissues. For example, certain ophthalmic surgical procedures require the cutting and/or removal of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibrils that are often attached to the retina. Therefore, cutting and removal of the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the choroid, a retinal tear, or, in the worst case, cutting and removal of the retina itself. Delicate operations such as mobile tissue management (e.g., cutting and removal of vitreous near a detached portion of the retina or a retinal tear), vitreous base dissection, and cutting and removal of membranes are particularly difficult.
The use of microsurgical cutting probes in posterior segment ophthalmic surgery is well known. Such vitrectomy probes are typically inserted via an incision in the sclera near the pars plana. The surgeon may also insert other microsurgical instruments such as a fiber optic illuminator, an infusion cannula, or an aspiration probe during the posterior segment surgery. The surgeon performs the procedure while viewing the eye under a microscope.
Standard vitrectomy probes typically include a hollow needle with a port on the end to pull in vitreous fibrils. An inner member, placed within the hollow needle, moves back and forth to open and close the port. This operates to cut any fibrils that enter the port while it is open. The rate at which the inner member moves with respect to the hollow needle is referred to as the cut rate. In some cases it is desirable to have a high cut rate. But, in some cases, it is desirable to have a relatively low, but more precise, cut rate. In some cases, it may even be desirable to perform a single cut. There is a need for continued improvement in the use and operability of vitrectomy probes. The systems discussed herein are arranged to address one or more of the deficiencies in the prior art.